Problem 19 - Chemistry The Central Science In Si Units

Question

In the process of attempting to characterize a substance, a chemist makes the following observations: The substance is a silvery white, lustrous metal. It melts at \(649^{\circ} \mathrm{C}\) and boils at \(1105^{\circ} \mathrm{C}\). Its density at \(20^{\circ} \mathrm{C}\) is \(1.738 \mathrm{~g} / \mathrm{cm}^{3}\). The substance burns in air, producing an intense white light. It reacts with chlorine to give a brittle white solid. The substance can be pounded into thin sheets or drawn into wires. It is a good conductor of electricity. Which of these characteristics are physical properties, and which are chemical properties?

Step-by-Step Solution

Answer

Physical properties: appearance, melting/boiling points, density, malleability, ductility, conductivity. Chemical properties: combustion, reaction with chlorine.

Step 1: Understand Physical Properties

Physical properties can be observed or measured without changing the composition of the material. Common physical properties include color, phase (solid, liquid, gas) at a certain temperature, density, melting and boiling points, malleability (ability to be pounded into sheets), ductility (ability to be drawn into wires), and electrical conductivity.

Step 2: Identify Physical Properties in Observations

Review the list of observations to identify which characteristics fall under physical properties. Here they are: 1) Silvery white, lustrous appearance (color and luster), 2) Melting point at 649°C, 3) Boiling point at 1105°C, 4) Density at 1.738 g/cm³, 5) Ability to be pounded into thin sheets (malleability), 6) Ability to be drawn into wires (ductility), 7) Good conductor of electricity (electrical conductivity).

Step 3: Understand Chemical Properties

Chemical properties describe a substance's ability to undergo a specific chemical change. These properties are observed when the substance interacts and forms one or more new substances. Examples include flammability, reactivity with other chemicals, and the type of product formed with such reactions.

Step 4: Identify Chemical Properties in Observations

Identify the characteristics that imply chemical changes: 1) Burns in air, producing intense white light (indicating a chemical change through combustion). 2) Reacts with chlorine to give a brittle white solid (a chemical reaction forming a new compound).

Step 5: Categorize Observations

Compile the identified properties: Physical properties include being silvery white, lustrous, melting and boiling points, density, malleability, ductility, and electrical conductivity. Chemical properties include burning in air and reacting with chlorine to form a new compound.

Key Concepts

Physical properties

Physical properties are aspects of a substance that can be observed or measured without altering its composition. They help define the characteristics of a material in its present form. For example, the color, state, and texture of a metal can be described without needing to change its chemical structure.

Physical properties are crucial for differentiating substances. They include parameters like:

• Melting and boiling points: These determine the temperatures at which a substance changes states. For instance, the substance mentioned has a melting point at \(649^{\circ} \text{C}\) and a boiling point at \(1105^{\circ} \text{C}\).
• Density: It measures how compact the material's mass is within a given volume. The substance in question has a density of \(1.738 \text{ g/cm}^3\).
• Color and lustre: These relate to the appearance of the substance, such as the silvery and lustrous attributes observed here.
• Electrical conductivity: This property indicates how well the substance allows electricity to pass through.

Understanding these physical properties helps scientists and engineers to select suitable materials for specific applications.

Malleability and ductility

Malleability and ductility are two physical properties that reveal how a metal might be manipulated into different shapes without breaking. They are intrinsic attributes for metals that are foundational in manufacturing and engineering.

Malleability refers to a metal's ability to be hammered or rolled into thin sheets. This quality is essential, especially in industries like automotive and construction, where components must be formed into precise shapes. In our example, the metal substance can be pounded into thin sheets, demonstrating good malleability.

Ductility is the ability of a metal to be drawn into wires. This flexibility is evident in electric cables and other industrial uses. The ability of the metal from our exercise to be drawn into wires emphasizes its ductility.

Understanding these properties helps in determining the application of a metal in processes where forming, shaping, or stretching metals is necessary.

Chemical reactions

Chemical reactions are processes by which substances interact to form new substances with different properties. These reactions are often accompanied by energy changes, producing indicators like light, heat, or gas formation.

In our exercise, the substance burns in air, emitting a bright white light, which is a sign of a chemical reaction known as combustion. This reaction involves the metal reacting with oxygen to form an oxide, producing heat and light as byproducts.

Another chemical property mentioned is its reaction with chlorine to form a brittle white solid. This interaction signifies a chemical change, as the metal reacts to form a new compound. Chemical properties like these are crucial for understanding how a substance might behave when mixed with other elements.

Through analyzing chemical reactions, chemists can predict how substances will behave in different environments, helping to innovate and apply them in various fields efficiently.